System and method for electrically controllable transmissions

ABSTRACT

Systems and methods are shown for electrically controllably transmitting power from a motor involving electrically controllably coupling the first input hub to a shuttle so that power is transmitted from the first input hub to the shuttle, providing for one-way rotation between the shuttle and a stationary chassis, and coupling the shuttle to an output hub with a spring such that energy is stored and released from the spring as the output hub rotates. Examples are shown that include controlling engaged and disengaged time intervals of the first input hub and shuttle to maintain a torque level at the output hub, such as by utilizing pulse width modulation or pulse frequency modulation. Examples are also shown involving electroadhesively coupling the first input hub to the shuttle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/746,762, filed Jun. 22, 2015, which claims the benefit of U.S.Provisional Patent Appl. No. 62/016,560, filed Jun. 24, 2014. Theforegoing applications are incorporated herein by reference.

BACKGROUND

The use of drives and transmissions in mechanical and electromechanicalsystems is quite common for such applications as transportation, motioncontrol, electronics, machine tools, printing machines, robotics andaerospace. When the load requirements are predictable, it is generallysimple to design a drive or transmission system with single or multiplegear stages. The situation becomes more complex when the loadrequirements vary and are unpredictable. Usually in these circumstances,the systems are designed with maximum anticipated values such as maximumanticipated speed and maximum anticipated torque. As a wide range oftorque and speeds need to be provided, the drive and transmissionsystems typically are larger in size, having more components and therebyincreasing the cost.

Robotic systems are one example of a context where these issues arise.Robots are currently being used in numerous applications and in numerousways. A few examples of their utilization may be found in industrialapplications where robots are used to perform repetitious or strenuoustasks and in medical applications sometimes to assist a surgeon inperforming surgery through teleoperation. For all their proliferation,robots are still limited in various ways.

One limitation which characterizes many robots is that they can onlyoperate a certain amount of time with a given battery size. One cause ofthis limitation is due to the losses that occur in the process ofconverting electrical energy to mechanical outputs. Improving theefficiency of conversion would then directly lead to longer operationtime with a given a battery size. In addition, the concepts to improveefficiency in mobile robots may be advantageous on stationary wallpowered robots as well. For example, improved efficiency may lead tosmaller motors thus leading to more compact design.

Yet another limitation that also characterizes many robots is that theyare often designed for the worst case load or speed conditions, makingthem big and bulky. Designing a robot that can quickly adapt to changingload conditions and operate with high efficiency would be desirable. Adesirable characteristic for many robotic systems is to have drivesystems that achieve high gear reduction ratios. Typically, inconventional systems, high gear reduction ratios are achieved byaddition of multiple gear stages. This adds weight to the system whichconsequently causes the inefficiencies to increase further which againcontributes to lower operating range or duration in the case of mobilerobots. Transmission systems with large gear reduction ratios in asingle stage are available commercially. However, these systems stillhave the disadvantages of being expensive and needing precisemanufacturing techniques.

Thus there is a need for efficient, light-weight, compact and fastactuating multispeed or variable transmissions which can be applied inactuators, manipulators, such as are used in robotics, and other devicesto address the needs stated above. Multispeed or variable transmissionshave been developed for a variety of applications but have not beenwidely used in robotics and other systems due to their complexity,volume and weight. Thus there is a need for single stage, efficient,light-weight, compact, low-cost drive systems which achieve high gearratio reduction. More advantages may be obtained by making thetransmissions variable.

In many applications, some as robots, since the speeds and torques ofmanipulators are highly cyclical and variable, using fixed gear ratiotransmissions results in high energy inefficiencies because the motor isusually operating away from its optimum efficiency speed. It also limitsthe range of forces and speeds the manipulator can operate at, oftenforcing a designer to oversize the motors in order to meet worst caserequirements. Just as a fixed-gear bicycle does not provide efficientlocomotion in hilly terrain, a fixed-gear-ratio transmission actuatorlimits the capabilities of a robotic joint and wastes energy

Minimizing the time it takes to change gear ratios also leads toadvantages since any delays would limit the speed at which themanipulator can change loads and as a result the range of tasks that itcan accomplish. For example, for a walking robot, the leg needs to movefast and with no load during the swing phase, but slower and with ahigher load during the stance phase of the stride. Similarly, during apick and place operation, a manipulator placing a heavy load will needto switch between high load/low speed and low load/high speed quickly toenable minimizing the cycle time.

Other advantages may be realized by being able to shift gear ratiosunder load and at zero speed to avoid limiting the range of tasks anactuator or manipulator can perform. Many existing transmission designscan only shift when they are in movement or not under load

SUMMARY

In one example, an electrically controllable transmission system isshown having a first input hub for receiving power from a motor or otheractuator and a first electrically controllable clutch with a firstportion coupled to the first input hub and a second portion, where thefirst and second portions may be electrically controllably coupled toone another such that power is transmitted from the first portion to thesecond portion. The second portion of the first electricallycontrollable clutch is connected to a shuttle and a bias member couplesthe shuttle to an output hub. A first one-way clutch also couples theshuttle to a stationary chassis or frame. In some examples, the firstand second portions of the electrically controllable clutch areconfigured to be electroadhesively engaged, such as where the firstelectrically controllable clutch is an electrolaminate disc clutch, anelectrolaminate activated wrap spring clutch, or an electromagneticallyactivated wrap spring clutch. In some examples, the bias member couplingthe shuttle to the output hub may be a torsional spring, a torsionaltube, or a combination.

In still other examples, the electrically controllable transmissionsystem includes a control circuit configured to control engaged anddisengaged time intervals of the first electrically controllable clutchto maintain a torque level at the output hub. In some examples, thecontrol circuit utilizes pulse width modulation or pulse frequencymodulation. Some examples may use a mechanical equivalent of a buckcircuit or a class D circuit to control the torque level.

In another example, the electrically controllable transmission systemalso includes a second input hub for receiving power from the motor anda second electrically controllable clutch with a first portion coupledto the second input hub and a second portion, where the first and secondportions are electrically controllably coupled to one another such thatpower is transmitted from the first portion to the second portion. Asecond one-way clutch couples the second portion of the secondelectrically controllable clutch to the second input hub. A shuttleconnects the second portion of the two controllable clutches together.The drive train from the motor is arranged so that the first input hubspins in one rotational direction and the second input hub spins in anopposite rotational direction. In other examples, the system furtherincludes a control circuit configured to control engaged and disengagedtime intervals of the first and second electrically controllableclutches to maintain a torque level at the output hub and the controlcircuit may be configured to control the engaged and disengaged timeintervals of the first and second electrically controllable clutchesusing a mechanical equivalent of a buck circuit or a class D circuit orusing pulse width modulation or pulse frequency modulation or acombination.

An example of a method for electrically controllably transmitting powerfrom a motor is shown that involves receiving power from a motor at afirst input hub, electrically controllably coupling the first input hubto a shuttle such that power is electrically controllably transmittedfrom the first input hub to the shuttle, providing for one-way rotationof the shuttle, and coupling the shuttle to an output hub with a biasmember such that energy is stored and released from the bias member asthe output hub rotates. In some examples of a method, the step ofelectrically controllably coupling the first input hub to a shuttlefurther includes electroadhesively coupling the first input hub to theshuttle, such as through the use of an electrolaminate disc clutch, anelectrolaminate activated wrap spring clutch, or an electromagneticallyactivated wrap spring clutch. In some examples, the step of coupling theshuttle to an output hub involves the use of a mechanical equivalent ofa buck circuit or a class D circuit or the use of a torsional spring, atorsion tube, or a combination.

In some examples of the method, the step of electrically controllablycoupling the first input hub to a shuttle involves controlling engagedand disengaged time intervals of the first input hub and shuttle tomaintain a torque level at the output hub, such as through the use ofpulse width modulation or pulse frequency modulation.

Other examples of the method for electrically controllably transmittingpower involve also receiving power from the motor at a second input hub,electrically controllably coupling the second input hub to the shuttlesuch that power is electrically controllably transmitted from the secondinput hub to the shuttle, and providing for one-way rotation between thesecond input hub and the shuttle, with the input drive train arrangedsuch that the first input hub spins in one rotational direction and thesecond input hub spins in an opposite rotational direction. In someexamples, the method includes controlling engaged and disengaged timeintervals of the first and second input hubs with the shuttle tomaintain a torque level at the output hub, such as through the use of amechanical equivalent of a buck circuit or a class D circuit or the useof pulse width modulation or pulse frequency modulation.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments in accordance with the present disclosure will bedescribed with reference to the drawings, in which:

FIG. 1A is a circuit diagram illustrating an example of a buck circuit;

FIG. 1B is a circuit diagram illustrating an example of a class Dcircuit;

FIG. 1C is a magnified view of signal 260 shown in FIG. 1B;

FIG. 2A is a circuit diagram illustrating an example of a mechanicalanalog of the buck circuit;

FIG. 2B is a circuit diagram illustrating an example of a mechanicalanalog of a class D circuit;

FIG. 2C is a graph illustrating an example of the operation of the buckcircuit of FIG. 2A;

FIG. 2D is a graph illustrating an example of the operation of the classD circuit of FIG. 2B;

FIG. 2E is a graph illustrating an example of a pulse width modulationscheme for controlling a transmission;

FIG. 2F is another graph illustrating the example of a pulse widthmodulation scheme for controlling a transmission;

FIG. 2G is yet another graph illustrating the example of a pulse widthmodulation scheme for controlling a transmission;

FIG. 2H is a graph illustrating an example of a pulse frequencymodulation scheme for a buck circuit;

FIG. 2I is another graph illustrating the example of a pulse frequencymodulation scheme for a buck circuit;

FIG. 2J is a graph illustrating an example of a pulse frequencymodulation for a class D circuit;

FIG. 2K is another graph illustrating the example of a pulse frequencymodulation for a class D circuit;

FIG. 3A is a cross-sectional view of a class-D mechanical analog;

FIG. 3B is an exploded perspective view of the device in FIG. 3A;

FIG. 3C is a perspective view of the device in FIG. 3A;

FIG. 3D is a cross-sectional view of a spring case;

FIG. 4 is a set of graphs illustrating examples of output hub torqueresponses when a load is driving an output of a class D analog;

FIG. 5A is a graph illustrating dead times in the operation of a clutch;

FIG. 5B is a circuit diagram illustrating an example of a circuit thatavoids both clutches from being activated at the same time;

FIG. 5C is a circuit diagram illustrating another example of a circuitthat avoids both clutches from being activated at the same time;

FIG. 6A is a cross-sectional view of an example of a mechanical analogto a buck circuit;

FIG. 6B is an exploded perspective view of the device in FIG. 6A;

FIG. 6C is a cross-sectional view of an example of a mechanical analogto class D circuit using wrap spring clutches;

FIG. 6D is an exploded perspective view of the device in FIG. 6C;

FIG. 7A is a representation diagram illustrating an example of aconfiguration of a buck circuit mechanical analog;

FIG. 7B is a representation diagram illustrating another example of aconfiguration of a buck circuit mechanical analog;

FIG. 7C is a representational diagram illustrating an example of ano-backlash system using two buck circuits;

FIG. 8A is a graph illustrating an example of output hub response;

FIG. 8B is a graph illustrating another example of output hub response;

FIG. 9A is a cross-sectional view of an example of a class D mechanicalanalog with a torsion tube;

FIG. 9B is a front view of a section of the engagement mechanism for thedevice in FIG. 9A;

FIG. 9C is a cross-sectional view of an example of the use of a coaxialtorsion tube;

FIG. 9D is a diagram illustrating an example of a plate that may be usedto couple the coaxial tubes of FIG. 9C;

FIG. 9E is a diagram illustrating an example of a ring that may be usedto couple the coaxial tubes of FIG. 9C;

FIGS. 10A and 10B are diagrams illustrating examples of electrolaminateclutches that may be used as electrically controllable clutches, such asthose illustrated in FIG. 3B; and

FIG. 11 is a functional block diagram illustrating an example of acontrol circuit.

Note that the same numbers are used throughout the disclosure andFigures to reference like components and features.

DETAILED DESCRIPTION

The subject matter of embodiments of the present invention is describedhere with specificity to meet statutory requirements, but thisdescription is not necessarily intended to limit the scope of theclaims. The claimed subject matter may be embodied in other ways, mayinclude different elements or steps, and may be used in conjunction withother existing or future technologies. This description should not beinterpreted as implying any particular order or arrangement among orbetween various steps or elements except when the order of individualsteps or arrangement of elements is explicitly described.

Examples are described herein of transmission systems that areelectronically controllable. Some examples of transmission systems useelectrolaminate disc clutches to transfer power from a motor to anoutput hub. While the examples discussed herein are described in thecontext of robotic systems, many aspects of the present examples may beadapted to a variety of applications where it is advantageous to provideactuators or manipulators that are efficient and light-weight, such asmotion control, electronics, machine tools, printing machines, microelectro-mechanical systems (MEMS), nano electro-mechanical systems(NEMS), and aerospace.

For example, in the field of robotics, systems are typically designedwith one motor per degree-of-freedom (DOF). Each motor would then besized for the maximum load/power requirements for its DOF. The resultingrobot would consequently carry more motor horsepower than it may need atany instant. Some aspects of the examples in this disclosure permitarchitectures with as few as one motor, sized to meet the maximum powerdemands of the entire robot. Further, the motors may run at a constantspeed thereby improving their efficiency. Some aspects of the examplesin this disclosure describe transmission methods to produce a variablespeed at the output hub, within an operating range, despite having asingle constant speed motor. The examples of transmission systemsdescribed in this disclosure differ from typical conventionalcontinuously-variable-transmissions (CVTs) and infinitely-variabletransmissions (IVTs) in that the conventional systems utilize relativelyslow, energy consuming methods of changing gear ratios. In contrast thetransmission system examples of this disclosure may offer fast methodsto change the gear ratio.

In some examples, the output hub of the present transmission systems mayonly rotate in one direction but the speed of the output hub may varycontinuously between zero and a maximum value. In some other examples,the output hub of the transmission system may rotate in both directionsand the speed of the output may vary between a maximum value in onerotational direction to a maximum value in the other rotationaldirection. A design goal of many robot systems is to minimize totalweight. However, as stated earlier, if a robot has multiple motors andeach motor is sized for maximum load/power requirements of a degree offreedom (DOF), then the total weight may be higher than desired. Hence,examples in this disclosure allow realization of robots and other typesof equipment that are lighter.

Several benefits may be realized with some of the transmission systemexamples described in this disclosure. For example, a robot builtutilizing the approaches described in this disclosure may have manyfewer motors and as few as one motor. This may enable a decrease in thetotal weight of the robot, leading to improved payload or range.Improved efficiency may also be obtained by running the motors at aconstant speed which becomes possible utilizing the examples describedbelow. Other benefits, in some examples, may include that by using acentralized motor system, motors may no longer need to be placed atextremities of the robot actuator systems such as a robot arm. Thisleads to lower inertia of these actuator systems which again leads toimproved efficiency and higher speed/acceleration of the arm.

Further benefits, in some examples, may include that by needing fewermotors, additional motors may be included in the robot architecture forredundancy without adding undue weight. Redundant motors in a multimotor system becomes impractical if each DOF is associated with its ownmotor.

Yet more benefits, in some examples, may include transmission systemsthat permit energy recovery. For example, for 2-legged robots that walk,energy may be recovered while deceleration of one leg occurs. Thisenergy may be used to power the acceleration of the other leg. These andother benefits of some of the examples will become clear from thedescriptions below.

Many conventional constantly variable transmissions (CVTs) andinfinitely variable transmissions (IVTs) exist. However, unlike theconventional transmissions, the examples described in this disclosureoffer rapid changing of transmission ratio under electronic control.Further the electronic control may be realized with a device (theelectrolaminate clutch) that is inexpensive and lightweight and requiresvery little power to drive it. This is in contrast to the heavy andenergy consuming methods of changing ratios in conventional CVTs andIVTs

Mechanically Switching Variable Transmission Systems

Variable transmissions are typically not used in robots because of theinability to achieve fast gear ratio changes and because of the largevolume and weight required to implement them. However, utilizing aspectsof the examples described below, the volume and weight requirements arereduced to practical ranges while providing a transmission that canchange gear ratios quickly and over a wide range of values. To help inunderstanding aspects of the examples, electrical analogies will beutilized. The use of electrical analogies for describing mechanicaldevices is well known. In this disclosure, the following analogs areused: the mechanical analog of a switch is a clutch, the mechanicalanalog of a diode is a one way overrunning clutch, the mechanical analogof an inductor is a torsion spring, the mechanical analog of a capacitor(connected to ground) is a rotational inertia (flywheel), the mechanicalanalog of electrical current is torque and the mechanical analog ofvoltage is rotational velocity. Other analogs are possible. To aid inunderstanding the variable transmission concepts, two electricalcircuits are briefly described below. Each circuit will then beassociated with different embodiments of the variable transmission.These two circuits, the buck circuit and the class-D amplifier circuit,are well described in the open literature so only the salient pointswill be described here. It is also to be noted that these two circuitsalthough closely related do have some differences which will bedescribed due to their pertinence to this disclosure

FIG. 1A illustrates a buck circuit. The heart of the circuit is thepower device 120 which may typically be a metal oxide semiconductorfield effect transistor (MOSFET). The transistor 120 is powered by apositive voltage V+. This terminal where the transistor is connected tothe V+ is commonly called the source terminal. An input signal 110 isfed into the transistor at the gate terminal. Further, a diode 160 isconnected to the third terminal which is numbered as 180 in the Figureand is commonly called the drain. Further, the terminal 180 is connectedto electrical ground via the diode as illustrated in the Figure. Thetransistor 120 simply acts as a switch in that the voltage at terminal180 ideally switches between V+ and 0 depending on the gate signal 110.The signal at terminal 180 is a magnified form of the signal 110 and isshown as 130 in the Figure. Terminal 180 is also connected to aninductor 140 and a capacitor 150 which form a low pass filter. Finally aload 170 is connected to the output of the low pass filter. The low passfilter filters out rapidly-changing signals so that the load only sees asmoother version of the signal 130. More details about the functioningof this circuit will be described below.

FIG. 1B illustrates a class D amplifier. The heart of the circuit arethe two power devices 225A and 225B. Typically these devices are metaloxide semiconductor field effect transistors (MOSFETs). These devicesare operated as binary switches and they are either ideally fully on orfully off but with only one switch being on at any instant of time. Theclass D amplifier is used to amplify input signals with high efficiency(i.e. with minimal generation of heat). In the Figure, an input signalis shown as a sinusoid 205 going into a comparator 215. The other inputof the comparator is a triangular signal 210 with a frequency muchlarger than the sinusoid. The output of the comparator is shown as abinary signal 245, where the width of each pulse encodes the inputsignal 205. Signal 245 is a representation of input signal 205 and iscalled a pulse width modulated signal. The signal 245 is fed as input tothe two MOSFETs 225A and 225B. The output of the class D circuit, whichis shown as 227 in the Figure, may be V+ or V− where V+ and V− are powersupply voltages. Due to the arrangement of the MOSFETs and the diodes230A and 230B, the output 250 is an amplified version of signal 245.Signal 250 is fed into a low pass filter formed by the inductor 235 andcapacitor 255 (LC circuit) which suppresses the high frequencycomponents in the signal 250. The final output signal is illustrated as260 appearing across a load 240. The signal 260 is an amplified versionof the input signal 205 with a small amount of superimposed ripple.

From the descriptions of the buck circuit 100 and the class D circuit200, it may be now evident that the two circuits are similar to someextent. One difference though is that the output of a buck circuitswings between 0 and V+ or alternatively between V− and 0 (provided thepower source is a negative voltage) and the output of the class Dcircuit swings between V+ and V−. In the mechanical analog which will bedescribed in detail below, the difference in the output between the twocircuits translates to the output of the mechanical analog of the buckcircuit rotating only in one direction and the output of the mechanicalanalog of the class D circuit rotating in both directions. Simplifiedmechanical models described below provide a more detailed explanation.

FIGS. 2A and 2B illustrate simplified mechanical models of the buckcircuit and the class D circuit respectively. To emphasize thesimilarity, some enumerated members in both Figures have the samenumbers. Both Figures show a single constant speed motor as 305. In FIG.2A, there is only a single coupling between the motor and the mechanicalanalog 322 of the buck circuit where as in FIG. 2B, the motor is coupleddirectly and via a reversing gear 310 to the mechanical analog 320 ofthe class D circuit. Terminal 317 of FIG. 2A corresponds to V+ in FIG.1A and terminal 315A and 315B correspond to V+ and V− in FIG. 1B. Theorder of correspondence between the terminals 315A and 315B and polarityof voltage V+ or V− is not material to this discussion. The switch 317in FIG. 2A corresponds to the transistor 120 in FIG. 1A and the switches319A and 319B in FIG. 2B correspond to the transistors 225A and 225B ofFIG. 1B. The inductors, resistors and the diodes are depicted in asimilar manner between FIGS. 1A and 2A and between FIGS. 1B and 2B. Box325 represents the load. FIGS. 2A and 2B illustrate that whereas thebuck circuit has only one switch, the class D circuit has two switches.In operation, which will be described below, any one of the switches ofthe class D circuit operates similar to the single switch of the buckcircuit so by understanding the operation of the buck circuit, theoperation of the class D circuit may be understood. Finally, it must benoted that in both the FIGS. 2A and 2B, the mechanical analog of theinductor is a spring and the mechanical analog of the diode is a one-wayclutch.

FIG. 2C illustrates the operation of the buck circuit of FIG. 2A withthe help of two graphs 330 and 335. Graph 330 illustrates the on offsequence of switch 327 as a function of time. When this switch is closed(i.e. when the clutch is engaged), the input at 317 is coupled to themechanical analog of the inductor 235 which is a spring, such that thespring will rotate in the direction of the motor. Referring to graph335, this graph refers to the conditions experienced by a load coupledto the spring. The load experiences a rise in the applied torque whenthe switch 327 is closed (or alternatively when the clutch correspondingto switch 327 is engaged). The spring stores energy during the timeswhen the switch is closed (or alternatively when the clutch is engaged),specifically during the Ton intervals. During Toff intervals when theswitch is off (alternatively when the clutch is disengaged), the springreleases its energy, still driving the load with torque decreasing overtime as indicated in graph 335 during these intervals. Hence it can nowbe seen that by alternately turning the switch on or off (oralternatively by causing the clutch to engage and disengage) and bychoosing the Ton and Toff intervals appropriately, a desired averagetorque output (340 in graph 335) may be obtained with a caveat that acertain amount of ripple may exist in the output torque. Note that aspring is one form of a bias member that elastically stores energy whendisplaced from its bias state and releases energy as it returns to itsbias state. Other forms of bias member may be utilized in variousexamples to achieve the inductive energy storage and return, which willbe appreciated by one of ordinary skill in the art.

FIG. 2D illustrates the operation of the class D circuit of FIG. 2B withthe help of three graphs 337, 338 and 339. As illustrated in FIG. 2B,there are two switches in the class D circuit hence the on-off sequenceof both are illustrated in graphs 337 and 338. These two switchescorrespond to clutches each of which when turned on, couples the directmotor input or the reversed motor input to the rest of the circuit. Ascan be seen in graphs 337 and 338, only one clutch is on at any oneinstant of time. As noted in the FIGS. 2B and 2D, clutch 319Bcorresponds to graph 337 and when this clutch is turned on, it causesthe load torque increase in the positive direction or in the directionof the motor spin. Similarly, clutch 319A corresponds to graph 338 andwhen this clutch is turned on, it causes the load torque to decrease(i.e. become more negative, which is the direction opposite thedirection of the motor spin) With this explanation, it can be seen ifclutch 319B is turned on and clutch 319A is turned off, for instance inintervals T1 and T3, the load experiences an increasing torque. Then,when clutch 319B is turned off and 319A is turned on for instance in theintervals T2 and T4, first the positive torque decreases and then thetorque in the negative direction increases. Thus for this specificexample, the load experiences an average torque as illustrated by thedashed line 341. Hence it can now be seen that by choosing the on-offsequence of both switches appropriately, a desired torque level may beachieved. A few more examples with different on-off sequence will now bedescribed.

Pulse Width Modulation

It can be seen from the above descriptions that any appropriate torquelevel may be achieved with an appropriate on-off sequence. This is truefor the buck circuit analog and for the class D circuit analog, thedifference being that the buck circuit can only provide torque in onedirection whereas the class D can provide torque in both directions. Inexamples described below the on-off sequence may be chosen in variousways. FIGS. 2E-2G describe various on-off sequences to obtain varioustorque outputs. These input sequences in these Figures fall in thecategory of pulse width modulated signals as the frequency of pulsing iskept the same but the width of the pulses vary. Only the graphs relatedto the class D are shown as the graphs related to the buck circuit aresimilar except for the difference of the available torque directionsdescribed above

FIG. 2E describes the same situation described in FIG. 2D except insteadof the clutch on-off times, graph 600 relates the input speed to theoutput speed for the class D case. During T1 for example, the positive(direct) input is switched in and during T2, the negative input isswitched in. Since all the time intervals are the same, the averageoutput speed illustrated by the dashed line at 605, is zero. Thefrequency of the pulsing is 1/(T1+T2) as all the intervals including T3and T4 are assumed equal.

FIG. 2F describes a situation where the positive rotation is switched infor a longer time than the reversed rotation while the frequency of thepulsing is kept the same as in FIG. 2E. As illustrated, T1 is 75% of theinterval T1+T2 although the frequency of pulsing is still 1/(T1+T2),assuming that T3 is equal to T1 and T4 is equal to T2. In this case, theaverage output speed as illustrated by the dashed line 615 may be equalto half the positive input speed.

FIG. 2G describes a situation where the positive rotation is switched onfor almost the whole interval T1+T2. The average output speed asillustrated by the dashed line 625 is almost equal to the positive inputspeed. The frequency of pulsing is still 1/(T1+T2).

Thus 2E-G illustrate various cases of pulse width modulated schemes.Pulse frequency modulation may also be employed and this is explained inrelation to the buck circuit for simplicity.

Pulse Frequency Modulation

FIGS. 2H and 2I illustrate the example of using pulse frequencymodulation for the buck circuit. Here, between the two graphs 630 and640, the width of the pulse T1 is kept the same but the frequency whichis 1/(T1+T2) is varied. T3 is equal to T1 and T4 is equal to T2 in bothgraphs. In graph 630, the average output speed is shown as 635 and ingraph 640, the average output speed is shown as 645. The average outputspeed in graph 640 is lower as the off times are larger than the ontimes. The interval T1+T2 may be varied, keeping the pulse width thesame at T1. Thus this scheme is called pulse frequency modulation as theinterval is varied but the width of the pulse is kept the same. The sametype of scheme may be applied to the class D circuit as well and isillustrated in FIGS. 2J and 2K.

In FIGS. 2J and 2K, graph 650 illustrates a first on-off sequence forthe class D analog. The first clutch is turned on at interval T1 wherebythe shuttle may assume the speed of the clockwise input. At interval T2,the second clutch may be turned on whereby the shuttle may assume thespeed of the counterclockwise input. As illustrated in graph 650, T1 maybe equal to T2. And the frequency is 1/(T1+T2). In comparison, referringto graph 660 of FIG. 2K, the width of the pulse T1 remains the sameexcept here T3 is larger than T2 of graph 650. Hence the frequency ofthe sequence in graph 660 which is 1/(T1+T3) is smaller than thefrequency of the sequence in graph 650. This scheme as before with thebuck circuit, is also called pulse frequency modulation as applicable tothe class D circuit.

In another example, it may also be possible to use a hybrid of the pulsewidth modulation and a pulse frequency modulation schemes

Mechanical Analog of the Class D Amplifier

FIG. 3A-C illustrate device that is a mechanical analog of a class Damplifier. FIG. 3A is a sectional view, FIGS. 3B and C are perspectiveviews. In this device, there is a central shaft or a pilot shaft 405that aligns the other components. There are two input hubs 410A and 410Bcorresponding to the V+ and V− inputs in FIG. 1B and also correspondingto 315A and 315B in FIG. 2B. These input hubs are where the output of asingle constant speed motor may be coupled into the device, one inputspinning in the direction of the motor and one input spinning in theopposite direction. Next, the device comprises of two electrolaminatedisc clutches 415A and 415B analogous to the transistors (MOSFETs) 225Aand 225B. Each clutch has two plates similar to the clutch described inthe companion disclosures. In FIG. 3B, the two plates of eachelectrolaminate clutch are clearly visible. Since the electrolaminateclutches depend on physical contact when a voltage is applied across theplates, springs 420A and 420B are included to the outside plate of eachclutch to allow for the motion of the plates towards each other whenvoltage is applied and to hold the outside plate at close proximity tothe inside plates, when voltage is not applied. The electrical circuitsthat enable the functioning of the electrolaminate clutches are notshown. For each clutch, the circuit may provide a voltage potentialacross the two plates much as in how voltage is applied to a capacitor.There are a number of ways to apply voltage across the plates of eachclutch. In one method, since the plates of the clutches rotate,electrical contact between the power supply such as a battery and eachplate may be made with brushes or slip rings. In another approach,portions of the device 400 that are shown in between the twoelectrolaminate clutches, such as the shuttle 425 (described in detailbelow) may be used as a common electrical ground and connected viabrushes or slip rings to a power source. Subsequently, the companionplates of each clutch may be connected via slip rings or brushes to thepower source via switches and other necessary electrical components.Regardless of how voltage is applied across the plates of the clutches,the (mechanical) output of each electrolaminate clutch is applied to oneway clutches 430A and 430B which correspond to the diodes 230A and 230B.These clutches are arranged so that the shuttle may rotate in eitherdirection but only as fast as the speed of the drive motor. The functionof these clutches will become more apparent as more elements of thedevice 400 are described.

The device 400 has a shuttle 425 which can spin about the pilot shaft405. The shuttle is coupled to a torsion spring 431 as is seen clearlyon FIG. 3B, though other forms of bias member may be utilized. The outerend of the spring is coupled to and contained within a spring case 435.The shuttle, the spring and the spring case can all rotate about thepilot shaft 405. The spring is analogous to the inductor 235 in FIG. 2B.The final output hub of the device is the gear 440. This is analogous to236 where the load resistor 240 is attached. The analog of the capacitoris not shown in FIG. 3A-C however, if needed, a flywheel (the analog ofa capacitor) may serve as an output.

For clarity, FIGS. 3 A-C does not show the detail of the spring case 435but this is now illustrated in FIG. 3D. The spring case may consist of ahollow chamber 436 through which the shuttle 425 and the pilot shaft 405may pass co-axially. The spring (not shown in the Figure) is coupled atone end to the shuttle 425 and to the walls of the hollow chamber 436 atthe other end. The hollow chamber may have a lid 437 which contains thespring within the hollow chamber. The lid may be coupled to the hollowchamber by bolts 438. The output gear 440 may be coupled to the springcase subsequently to either side of the hollow chamber. As statedearlier, the device 400 has two inputs which rotate in oppositedirections. Each input may be coupled to the shuttle by activating thecorresponding electrolaminate clutch 415A or 415B. For example, clutch415A may couple the input at 410A and clutch 415B may couple the inputat 410B.

Clutch 415A includes disk pair 416A and 417A and clutch 415B includesdisk pair 416B and 417B, which form electrically controllable clutches.Depending upon the technology used, one or both of the disks in eachdisk pair may be electrically activated to increase traction between thedisks of the disk pair and engage the clutch 415A or 415B. Ifelectroadhesion is utilized, one disk of each disk pair may be activatedto produce traction, as discussed in further detail with respect toFIGS. 10A and 10B.

Noting that only one clutch may be engaged at any instant of time, anexplanation of the sequence of events when one clutch is engaged is nowdescribed. The sequence of events when the other clutch is engaged issimilar. Also, for the sake of clarity, the input at 410A is assumed tobe a positive or clockwise input provided by a constant speed motor (notshown in the Figure) also spinning clockwise or in a positive direction.The actual direction of the input whether it is clockwise oranticlockwise is not material to this discussion as long as it isunderstood the other input 410B is rotating opposite of the input at410A. Assuming that input hub 410A is coupled directly to a constantspeed motor, when clutch 415A is engaged (and 415B is not engaged), itcouples the direct input to the shuttle.

The spring winds up in the direction of the input rotation which isclockwise according to the assumption above. In this phase when clutch415A is engaged, the spring may store energy and may also drive a loadconnected to the output gear 440. The load may experience a risingtorque in the direction of the motor rotation (positive or clockwise) asillustrated in FIG. 2D, graph 339. Next, if the clutch 415A isdisengaged and the clutch 415B is engaged, the spring unwinds and beginswinding up in counterclockwise or negative direction, decreasing thetorque in the clockwise direction and subsequently applying a torque inthe counterclockwise or negative direction. Thus as explained earlier,by choosing the on-off sequence of the clutches appropriately, anydesired torque between the maximum and minimum limits of torque may beobtained. The function of the one-way clutches is now further described.

Returning back to the scenario when the electrolaminate clutch 415A isengaged and the electrolaminate 415B is disengaged, the one way clutch430A allows the electrolaminate clutch 415A to drive the shuttle in thedirection of the clockwise input rotation as assumed in the exampleabove. Thus the spring winds up in a clockwise direction. The other endof the shuttle closest to the counterclockwise or negative input, alsohas a one way clutch 430B but it does not prevent the shuttle fromrotating clockwise next to the counter rotating half of the disengagedelectrolaminate clutch 415B. However when the electrolaminate clutch415A is disengaged and the electrolaminate clutch 415B is engaged, nowboth plates of the electrolaminate clutch 415B may move in acounterclockwise direction, opposite of the direction of the clockwisewound up spring. The clockwise wound up spring will now unwind in acounterclockwise direction however, it may unwind no faster that thespeed of the counterclockwise rotating electrolaminate clutch 415B andthe one way clutch 430B. The one way clutch 430A acts in the same way asabove except with the relevant directions reversed—hence thisexplanation will not be provided. From the above explanation, thefunction of the one way clutches is now clear.

It was briefly mentioned above that in some cases a flywheel may serveas an output hub of the device 400. Two considerations regarding thisarrangement are now provided. In the first consideration, referring toFIG. 1B, the electrical class D circuit incorporates a capacitor 255connected between the amplifier output terminal 236 and the electricalground 238. The mechanical analog of an electrical ground is inertialspace. In other words, the position of the flywheel (which serves as theanalog of the capacitor) is measured in relation to a fixed frame ofreference. All other inertial components of the system may also bereferred to this common reference frame. In FIG. 1B, the common groundis denoted by 238.

In the second consideration, a flywheel has been described earlier asthe mechanical analog of the capacitor. The flywheel may simply beviewed as a component that has inertia. In a typical robot, referring toFIG. 2B, the output terminal 236 (a rotating shaft for example), may beconnected to the remainder of a robot DOF. Typically this may comprise agear train followed by a robot limb (e.g. an arm). A robot arm may ormay not be carrying an inertial load, and may experience additionalviscous loads which are directly analogous to the resistive load 240 ofFIG. 1B. All gear trains have rotational inertia and internal losses dueto friction and lubricants. The inertia is analogous to a capacitor andthe internal losses are analogous to a resistive load. In addition,inertia of the arm together with any inertial load are effectively added(after an adjustment due to the gear ratio) to the transmissioninertial. The viscous loads are added to the transmission losses. Whenall these effects are considered, depending on the specific requirementsof the application, it may often be feasible to use a mechanism such asin FIG. 3A which does explicitly include a flywheel or viscouscomponent. By excluding a flywheel, the weight, size and cost of themechanism are reduced which is advantageous in general but specificallyin the design and manufacture of robots. If the system with a singleflywheel results in precession issues, a second flywheel may be coupledspinning in the opposite direction, thus reducing or eliminatingprecession.

It is to be understood though that despite the discussion aboveregarding the advantages of not having flywheels, its use is notprecluded in some applications

Load Driving the Motor

FIG. 2E-G illustrate graphs when the output gear 440 of device 400 isdriving the load. With most robots, during certain tasks, the load maydrive the motor via the transmission. This case is illustrated in FIG. 4where four graphs 700, 705, 710 and 715 are shown. As graph 700indicates, T1≅T2 such that (ω_(out)≅0 but ω_(out)>0. During interval T1,in cases where the load may be driving the motor, the output speed maybe positive but the output torque as shown in graph 705 may be negativewhich indicates that power flowing backwards. Another description ofthis condition is that instead of the constant speed motor applyingpower to the load through the device 400, the load is applying powerback to the motor. This power may be utilized for example to charge abattery associated with the motor or to accelerate the motor to a higherspeed. For convenience for the ensuing description referring to FIG. 3A,the left side of the Figure is called the positive side and the rightside of the Figure is called the negative side. Thus the input hub 410Ais called the positive input hub and the input hub 410B is called thenegative input hub. The one-way clutch 430A is called the positiveone-way clutch and the one-way clutch 430B is called the negativeone-way clutch.

During time interval T1, as graph 700 indicates, the shuttle speed willassume the speed of one of the input hubs. The graph 700 indicates thatthe shuttle assumes the speed of the positive input hub during timeinterval T1. During this time interval, the spring 431 of FIG. 3A willbe winding because the speed of the shuttle is +ω_(in) and the speed ofthe output hub is nearly zero. Thus the net rotational velocity of thespring is ω_(shuttle)−ω_(out). In addition, in this case, the springtransmits the output torque to the output, which exerts this same torqueon the load. Due to the negative output torque with the speed of theshuttle equal to the speed of the driving motor, the positive one-wayclutch is engaged, transmitting a torque roughly equal to the outputtorque. This is shown in graph 710 during T1. This clutch torque is thensubsequently experienced by the motor. As a result, the motor, in theabsence of any other torques such as those caused by the motor drivesignals, will accelerate. Thus, energy is transferred from the load tothe motor, increasing the motor kinetic energy. During this time T1, thenegative one-way clutch (or the clutch associated with the negativeinput hub) will not experience a torque as it is designed to bedisengaged when the shuttle speed is more positive than −ω_(in).

The energy that is transferred to the motor may be used in either of thetwo methods described below or in combination: In the first method, thekinetic energy may be used in a subsequent movement of the robot so thatless battery energy is used. For example, a robot doing a deep kneebend, energy that is recovered from the load on the way down is storedas kinetic energy in the motor rotor. Then, when the robot is moving up,the kinetic energy is used to lift the load against gravity. In a secondmethod, the energy may be used to recharge the battery as the motor actsas a generator. Most conventional robots are able to accomplish thesecond method described above however, the class D analog mechanismdescribed in this disclosure can accomplish both the methods.

For completeness, the behavior of the device during time T2 is nowdescribed. During this time, the negative electrolaminate clutch isengaged. This clutch forces the shuttle velocity to be −ω_(in), thespeed of the negative input hub. Due to this shuttle speed, the positiveone-way clutch is disengaged and its torque is zero as shown in graph710. During time T2, the negative shuttle torque is provided by themotor via the negative electrolaminate clutch. This torque is not shownin FIG. 4.

Hence in certain situations for example in a humanoid robot which may berun on battery power, generating energy to extend the battery life maybe advantageous and the above example may be a way to realize thisadvantage.

Dead Time

As with any circuit or mechanism, the ideal behavior of theelectrolaminte clutches and their practical behavior differ in someaspects. In particular, as with all clutches of any type, theelectrolaminate clutch may have an engagement or a disengagement delay.In other words, there may be a time delay between when an electricalsignal is sent to engage the clutch and when the clutch is mechanicallyengaged. Similarly, there may be a delay between when an electricalsignal is sent to disengage a clutch and when the clutch is actuallymechanically disengaged. Some other characteristics of the time delaysare that the engagement and disengagement delay may not be equal to oneanother. Further, the engagement (or the disengagement) delay may differfrom one engagement (or disengagement) to another. There are severalconsequences of these time delays. One consequence is that if thesedelays are not accommodated for in terms of the on-off sequence of theclutches and if both clutches are effectively engaged at the same time,the result may range from a loss of efficiency to malfunction ordestruction of the device. To avoid these consequences, a “dead time”may be purposely introduced in the on-off sequence of the clutches suchthat an engaged clutch is mechanically disengaged before an electricalsignal is provided to the disengaged clutch for it to engage. FIG. 5Aillustrates this example. The graph 800 illustrates a first clutch goingfrom an engaged state to a disengaged state. A period of timeillustrated as T_(dead) is allowed to elapse before the clutch in graph810 is turned on. Although these graphs show ideal behavior of theclutches in that they turn on and off instantaneously, the approach isthat T_(dead) may be adjusted to accommodate the engagement anddisengagement delays of the clutches. The dead time may be about 0.5 to10 msec. but other values are possible. Further, this value may bechosen based on the detailed understanding of the behavior of theclutches and other members of the device 400 as described below.

Referring to FIG. 3A, the situation when clutch 415A is engaged and 415Bis disengaged is now considered. The situation when 415B is engaged and415A is disengaged is essentially identical in concept and will not bedescribed. First and electrical signal to disengage the clutch 415A isapplied. After a dead time interval, a signal to engage clutch 415B isapplied. Based on the disengagement delay of clutch 415A, this clutchbecomes mechanically disengaged and the shuttle 425 is able to rotatefreely. Assuming that the spring was wound up clockwise when 415A wasengaged, when it becomes disengaged, the spring will unwind in thecounterclockwise direction, and apply a negative torque (in thecounterclockwise direction) on the shuttle. The shuttle will experiencea rapid negative acceleration under the influence of the spring until itreaches the counterclockwise speed of the input hub 410B. At this point,one-way clutch 430B will engage constraining the shuttle to rotate atthe same speed as the input hub 410B. Now, while clutch 430B is engaged,clutch 415B will mechanically engage after its own engagement delay haselapsed. At the instant of mechanical engagement, the velocitydifference of the two plates of clutch 415B may be zero or close tozero. As a result of this, the energy lost due to clutch friction iszero or close to zero and the clutch wear should be minimal. Hence usingthe above discussion as a guideline, T_(dead) may be advantageouslychosen to ensure that the on-off sequence of clutch engagement anddisengagement results in maximizing mechanism lifetime and efficiency.

Some methods are now described to ensure that both clutches are notengaged at the same time. In FIG. 5B, a computer 825 generates a pair ofon-off sequences and outputs these sequences via outputs 830 and 835.The outputs 830 and 835 are each coupled to hardware circuits 840 and845 which may also communicate with each other as illustrated by thebidirectional arrow 860. The input hub of the hardware circuits may thenbe coupled to clutches 850 and 855 (or alternatively clutches 415A and415B of device 400). In a first variation of this example, the computerprogram may simply ensure that the on-off sequence is appropriate andthe two clutches are never turned on at the same time. However, toprovide a failsafe method, the hardware circuits may ensure that onlyone clutch 850 or clutch 855 may be turned on at any one time. Variouswell known methods are known to achieve this type of result. FIG. 5Cillustrates just one method. Each of the two outputs 830 and 835 fromthe computer may be coupled to an inverter. Thus, output 830 may becoupled to inverter 865 and output 835 may be coupled to inverter 860.The output of the inverters may be input to one end of a AND gate. ThusAND gate 870 may perform a logical AND operation between output 830 andan inverted output 835. Similarly, AND gate 875 may perform a logicalAND between output 835 and an inverted output 830. The output of the ANDgates are used to activate clutches 850 and 855 on (or alternativelyclutches 415A and 415B of device 400). The configuration in FIG. 5Censures that when both outputs 830 and 835 are high, the outputs of theAND gates are low, which is a permissible state for the operation of thedevice 400 of FIG. 3A.

Alternate Constructions of the Mechanically Switching VariableTransmission

FIG. 3A-C illustrate the mechanically switching variable transmissionwhich as stated above is the mechanical analog of the class-D amplifier.It was also stated above that a buck circuit is a close relative of theclass D circuit and the two circuits were described in FIGS. 1A and 1B.Now in another example, a device based on the buck circuit isillustrated in FIGS. 6A-B. As expected, this device is similar to device400 of FIG. 3A. To emphasize the similarity in the devices 400 of FIG.3A and 450 of FIG. 6A, components that are similar between the twodevices have been given the same enumeration. Due to the similaritybetween the two devices, the differences will be described below. Thedevice 450 of FIG. 6A, the buck circuit analog, may have only one inputhub shown at 410A. Consequently, the device 450 may provide torque onlyin one direction. Since there is only one input hub, the device 450 mayhave only one electrolaminate clutch and only one one-way clutch whichare shown as 415A and 430A. On the other side of the device (opposite ofthe side which has the input hub), the device 450 has an output gear orhub 440 just as in the device 400, which in this case only rotates inone direction. Also just as in the device 400, the device 450 has ashuttle 425 which rotates on bearing 432. As seen in FIG. 6A, at theleft end of the shuttle, a one-way clutch 430B is mounted so that itoperates between a non-rotating collar 433 and the shuttle. This isanalogous to the diode 160 of FIG. 1A. FIG. 6B shows an exploded view ofthe device in FIG. 6A. The functioning of the device 450 has beendescribed earlier and is similar to the functioning of the device 400(class D analog) except for the available directions of torque androtation. In addition, the application of voltage across the plates ofthe electrolaminate clutch 415A is accomplished in a similar manner asin device 400 of FIG. 3A.

Devices which Use Alternate Types of Clutches

In another example, the devices 400 and 450 may use alternate types ofclutches other than the electrolaminate enabled clutch. As an example,these devices may use wrap spring clutches as described in FIGS. 6C and6D. The device 900 is similar to device 400 of FIGS. 3A-C except thedevice 900 is shown using wrap spring clutches. The wrap spring clutchesare shown as 910A and 910B and may couple two shafts when activated. Asthe device 900 is class D analog, it has two inputs 410A and 410B. Onthe left side of FIG. 6C, the wrap spring clutch 910A couples the input410A and the shuttle 425. Similarly on the right side of the Figure, thewrap spring clutch 910B couples the input 410B and the shuttle 425. Allother details remain the same between device 400 and device 900. It mustalso be noted that the buck circuit analog illustrated in FIGS. 6A-B mayalso use the wrap spring clutch instead of the electrolaminate discclutch. As in devices 400 and 450, the electrical activation of the wrapspring clutches may be accomplished via slip rings or brushes.

Combination of Buck Circuit Analogs

In another example, two buck circuit analogs may be used in a mechanicalcircuit to achieve a method to pull in two directions. Pulling in twodirections is an advantageous feature in many situations such as but notlimited to an arm of a robot where the arm may need to be controlled inopposite or antagonistic directions. FIG. 7A illustrates one variationof this example. Many of the components in FIG. 7A are similar to thecomponents in FIGS. 2A and B and thus the same enumeration is utilized.305 is a constant speed motor and 310 is a reversing gear. 1005A and1005B are mechanical analogs of the buck circuit and are similar to 322in FIG. 2A however a different enumeration is used for clarity ofexplanation. 1010A and 1010B are clutches which may couple the output of1005A and 1005B to the step-down transmission 1015. The final output ofthis arrangement is shown as 1020, which may be an output hub. Theclutches 1010A and 1010B may be of the types described in thisdisclosure such as the electrolaminate disc clutch or the wrap springclutch. It may be of other types as well such as those availablecommercially. The inductors in 1005A and 1005B correspond to springs andthe diodes correspond to one-way clutches as described earlier. Forclarity the output 1025A of the motor 305 may be assumed to be clockwiseand the output 1025B may be assumed counterclockwise. The actualdirections may be reversed and is immaterial to the ensuing discussion.The arrangement in FIG. 7A illustrates that with two buck circuits, thefinal output hub 1020 may be caused to move in a clockwise or acounterclockwise direction. When the buck circuit analog 1005A is turnedon and 1005B is turned off, output hub 1020 may move in a clockwisedirection. Similarly when the buck circuit analog 1005B is turned on and1005A is turned off, output hub 1020 may move in a counterclockwisedirection. The function of the clutches 1010A and 1010B is nowdescribed. The function of these clutches is described with a specificexample of when the buck circuit 1005A is turned on and 1005B is turnedoff. In this situation, the clockwise input is coupled to the output hub1020. However in this situation if clutch 1010B is not disengaged, theone-way clutch in 1005B will prevent the output hub from turning in theclockwise direction. The situation is similar with regards to the outputhub moving in the counterclockwise direction. Thus, to cause the outputhub 1020 to rotate in any specified direction, the clutch associatedwith the other direction needs to be disengaged. The speed of rotationof the output hub will depend on the pulse sequence applied to the buckcircuit analog 1005A and 1005B. To stop the output hub 1020 fromrotating, if 1005A and 1005B are turned off but if the clutches 1010Aand 1010B are left engaged, the one-way clutches in 1005A and 1005B willprevent the output hub 1020 from rotating. Thus it is clear how twodirections of rotation may be achieved with the arrangement describedabove.

In yet another example, pull in two directions may be achieved by thearrangement shown in FIG. 7B. In this case only one buck circuit analog1005A is coupled to the clockwise output 1025A of the constant speedmotor. One output of the buck circuit analog 1005A is then subsequentlycoupled to a clutch 1010A. However the output of the buck circuit isalso coupled to a reversing gear 310 which is then coupled to anotherclutch 1010B. Thus the final output hub 1020 may be caused to move inthe clockwise or counterclockwise direction depending on which of thetwo clutches 1010A or 1010B is turned on. Clutch 1035 is illustrated inthe Figure such that one side of the clutch is coupled to ground. Thisclutch enables the configuration 1030 to stop the output hub 1020 fromrotating. Additionally, the speed of rotation of the output hub willdepend on the pulse sequence applied to the buck circuit analog 1005A.Thus it is clear how two directions of rotation may be achieved with thearrangement described above.

In yet another example, in a variation of the configuration 2000illustrated in FIG. 7A, another configuration is illustrated in FIG. 7C.In this configuration, backlash may be eliminated. Two step downtransmissions 1017A and 1017B are provided in this configuration wherethe output of each step down is coupled to small gears 1018A and 1018B.Both small gears are coupled to one large gear output hub 1019.Elimination of backlash is now described with a specific example.Assuming that the buck circuit 1005A is turned on and couples theclockwise output of the motor 305 to the small gear 1018A, the outputgear 1019 will turn counterclockwise. In this example, the small gear1018B may be also turned on but with a small torque. Thus by driving onesmall gear in one direction with a large torque and by driving the othersmall gear in the opposite direction with a small torque, backlash maybe eliminated.

Mathematical Analysis and Procedure for Spring Design

Additional examples are described in later sections based on themathematical analysis below. Different cases are considered so that thedevice 450 may be better designed. For the following mathematicalanalysis, the following nomenclature will be used:

ω_(in,) Input speed of transmission ω_(out) Output speed of transmissionT_(in) Input torque of transmission T_(out) Output torque oftransmission T_(r) Torque ripple T_(max) Maximum torque at transmissionoutput c Fraction relating T_(r) to T_(max) t₁ Minimum engagement timeof clutch t₂ Minimum disengament time of clutch k Spring constant oftorsion spring σ_(max) Maximum design stress in spring E Young's modulusof spring b Axial length of torsion spring h Thickness of torsion springl Length of torsion spring ρ Density of torsion spring material M₀Moment acting on the spring Q Moment of inertia

CASE1: ω_(out)≈0 but ω_(out)>0 and T_(out)=T_(a) where T_(a)<T_(max).Referring to FIG. 8A, during the time t₁, the spring will be woundthrough an angle:θ=t ₁ω_(in)  Eqn. 7

The corresponding increase in torque is:ΔT=T _(r) =Kθ=kt ₁ω_(in)  Eqn. 8

T_(r) is the torque ripple and is illustrated in FIG. 8A. Smoothertorque output will require that T_(r) be a small fraction c of T_(max).Typically c may be chosen in the range 0.01≤c≤0.1 although other rangesare possible. Thus

$\begin{matrix}{{{{kt}_{1}\omega_{in}} = {T_{r} < {cT}_{\max}}}{and}} & {{Eqn}.\mspace{14mu} 9} \\{k < \frac{{cT}_{\max}}{t_{1}\omega_{in}}} & {{Eqn}.\mspace{14mu} 10}\end{matrix}$

CASE 2: ω_(out)≈ω_(in) but ω_(out)<ω_(in) and T_(out)=T_(a) whereT_(a)<T_(max). Referring to FIG. 8B, during the time t2, the spring willunwind through an angle:θ=−t ₂ω_(out) ≅−t ₂ω_(in)  Eqn.11

The corresponding decrease in torque is:ΔT=T _(r) =Kθ=−kt ₂ω_(in)  Eqn. 12

Using the same steps as in case 1, it can then be concluded that

$\begin{matrix}{k < \frac{{cT}_{\max}}{t_{2}\omega_{in}}} & {{Eqn}.\mspace{14mu} 13}\end{matrix}$

Equations 10 and 13 indicate that if t₂≅t₁, the spring constant for case2 will be similar to the value computed for case 1.

CASE3:

$\omega_{out} = {{\frac{\omega_{in}}{2}\mspace{14mu}{and}\mspace{14mu} t_{1}} = t_{2}}$

In this case, during engagement, one end of the torsion spring isrotating at ω=ω_(in) while the output end of the spring rotates at

$\omega = {\frac{\omega_{in}}{2}.}$Hence the net windup rate is:

Windup rate:

$\begin{matrix}{{\omega_{in} - \frac{\omega_{in}}{2}} = \frac{\omega_{in}}{2}} & {{Eqn}.\mspace{14mu} 14}\end{matrix}$

Similarly, during clutch disengagement, the unwinding rate is

Unwinding rate:

$\begin{matrix}{- \frac{\omega_{in}}{2}} & {{Eqn}.\mspace{14mu} 15}\end{matrix}$

Thus, the angle the spring unwinds is:

$\begin{matrix}{\theta = \frac{{- t_{2}}\omega_{in}}{2}} & {{Eqn}.\mspace{14mu} 16}\end{matrix}$

The torque ripple in this case is:

$\begin{matrix}{T_{r} = {{k\;\theta} = \frac{{kt}_{2}\omega_{in}}{2}}} & {{Eqn}.\mspace{14mu} 17}\end{matrix}$

It can be seen by comparing Eqn. 17 to Eqn. 8 and Eqn. 12, when t₁=t₂,the torque ripple is halved which is advantageous. As will be describedbelow in some detail, the energy loss during the process of engagementand disengagement is proportional to the frequency of the pulses. Thismay be readily understood when t₁=t₂ however is not necessary for t₁ tobe always equal to t₂. Thus by decreasing the frequency for example byhalving it, the energy loss may be halved. Operating the devices whenthe torque ripple is halved and when the energy loss may be low, is anadvantageous mode of operation.

Energy Loss in the Process of Engagement

To analyze the energy loss during engagement and disengagement, thefollowing additional variables may be defined:

I_(s) Combined inertia of the clutch driven disk, the shuttle and theend of the spring attached to the shuttle.

T_(e) The torque that is transmitted by the clutch

ω_(d) Speed of the driven disk

t_(e) Clutch engagement time

Then during engagement,

$\begin{matrix}{\frac{d\;\omega_{d}}{dt} = \frac{T_{e}}{I_{s}}} & {{Eqn}.\mspace{14mu} 18}\end{matrix}$

Assuming that ω_(in) is constant regardless of the load imposed by theclutch, ω_(d) reaches ω_(in) after a time t_(e) given by:

$\begin{matrix}{t_{e} = \frac{\omega_{in}I_{s}}{T_{e}}} & {{Eqn}.\mspace{14mu} 19}\end{matrix}$

The assumption is consistent with a motor with large inertia. It is alsoto be noted that for these discussions, t_(e)<<t₁.

During the engagement process that lasts for an interval equal to t_(e)the energy supplied by the motor is power times duration. Thus:

$\begin{matrix}{{\Delta\; E_{motor}} = {{T_{e}\omega_{in}t_{e}} = {{T_{e}\frac{\omega_{in}^{2}I_{s}}{T_{e}}} = {I_{s}\omega_{in}^{2}}}}} & {{Eqn}.\mspace{14mu} 20}\end{matrix}$

On the assumption that prior to engagement, the clutch disk and shuttlewere at rest and after engagement, they spin with a velocity of ω_(in),the energy gained by the clutch/shuttle assembly may be given by:ΔE _(shuttle)=0.5I _(s)ω_(in) ²  Eqn. 21

Based on Eqn 21, it can be concluded that the energy lost due tofriction (ΔE_(eng. friction)) must be:

$\begin{matrix}{{\Delta\; E_{{eng}.{friction}}} = {{{\Delta\; E_{motor}} - {\Delta\; E_{shuttle}}} = \frac{I_{s}\omega_{in}^{2}}{2}}} & {{Eqn}.\mspace{14mu} 22}\end{matrix}$

From Eqn. 22, it can thus be seen that the energy loss due to frictionis independent of the clutch engagement time t_(e) or torque T_(e). Thisis a consequence of the fact that the clutch engagement may be similarto an inelastic collision. For such a collision, the amount of energylost is independent of the detailed time history of the collisionitself.

Energy Loss in the Process of Disengagement

To analyze the energy loss during disengagement, the followingadditional variables may be defined:

t_(d) Clutch disengagement time

T_(d) Torque exerted by the clutch during disengagement

To analyze the energy loss due to clutch disengagement, an assumptionthat a fixed torque T_(d) is exerted by the clutch needs to be made.Unlike the case for engagement, the disengagement time t_(d) is notconstrained by an equation such as Eqn. 19 for t_(e). The variable t_(d)is essentially a characteristic of the clutch. A further assumption thatt_(d)<<t₁ or t₂ is made to clarify the understanding of energy lossduring disengagement. During this process of disengagement, the shuttlewill not significantly decelerate during the interval t_(d). However, tocomplete the analysis, another assumption needs to be made about theinput-to-shuttle speed difference after the time interval t_(d). To gaina conservative estimate about the energy loss during disengagement, anoverestimation of the speed difference may be made. Another way tounderstand this scenario is that the shuttle does not loose appreciablespeed after disengagement. Hence with these assumptions, the energy lostdue to clutch friction during disengagement may be written as:

$\begin{matrix}{{\Delta\; E_{{dis}.{friction}}} \leq {{T_{d}\left( {\omega_{in} - \frac{9\;\omega_{in}}{10}} \right)}t_{d}}} & {{Eqn}.\mspace{14mu} 23} \\{{\Delta\; E_{{dis}.{friction}}} \leq \frac{T_{d}t_{d}\omega_{in}}{10}} & {{Eqn}.\mspace{14mu} 24}\end{matrix}$

From Eqn. 19

$\begin{matrix}{t_{e} = \frac{\omega_{in}I_{s}}{T_{e}}} & {{Eqn}.\mspace{14mu} 25}\end{matrix}$

On the assumption that t_(d)=t_(e) and T_(d)=T_(e) then

$\begin{matrix}{t_{d} = \frac{\omega_{in}I_{s}}{T_{e}}} & {{Eqn}.\mspace{14mu} 26}\end{matrix}$

Substituting Eqn. 26 in Eqn. 24

$\begin{matrix}{{\Delta\; E_{{dis}.{friction}}} \leq \frac{{T_{d}\left( \frac{\omega_{in}I_{s}}{T_{e}} \right)}\omega_{in}}{10}} & {{Eqn}.\mspace{14mu} 27} \\{{\Delta\; E_{{dis}.{friction}}} \leq \frac{I_{s}\omega_{in}^{2}}{10}} & {{Eqn}.\mspace{14mu} 28}\end{matrix}$

Comparing Eqn. 28 with Eqn. 22, the following equation may be writtenΔE _(dis.friction)≤(⅕)ΔE _(eng.friction)  Eqn.29

From Eqn. 29 it can now be seen that the energy loss at clutchdisengagement may be small or negligible compared to energy loss duringengagement. From the preceding analysis it can also be stated thatenergy loss due to clutching is proportional to I_(s). Hence it may beadvantageous to reduce the inertia I_(s). Description of the examplesrelated to low inertia shuttles will be described in later sections ofthis disclosure.

Procedure for Design of the Spring

The following procedure describes how to design a practical springfollowing the calculation of k from the above equations. From Kent'sMechanical Engineers' Handbook (Design and Production Volume, TwelfthEdition, 1950, Colin Carmichael, ed., pages 11-26 to 11-28) for ahelical torsion spring,

$\begin{matrix}{{\theta = \frac{M_{0}l}{EQ}}{Since}} & {{Eqn}.\mspace{14mu} 30} \\{k \equiv \frac{M_{0}}{\theta}} & {{Eqn}.\mspace{14mu} 31}\end{matrix}$

Substituting Eqn. 30 in Eqn. 31 gives

$\begin{matrix}{k = \frac{EQ}{l}} & {{Eqn}.\mspace{14mu} 32}\end{matrix}$

From Kent's Handbook,

$\begin{matrix}{Q = \frac{{bh}^{3}}{12}} & {{Eqn}.\mspace{14mu} 33}\end{matrix}$

Substituting Eqn. 33 in Eqn. 32 gives

$\begin{matrix}{k = \frac{{Ebh}^{3}}{12\; l}} & {{Eqn}.\mspace{14mu} 34}\end{matrix}$

Also from Kent's Handbook,

$\begin{matrix}{\sigma_{\max} = \frac{6\; M_{0}}{{bh}^{2}}} & {{Eqn}.\mspace{14mu} 35}\end{matrix}$

Based on this the following method to design a spring may be followed.

Step 1: Pick an initial reasonable value for b.

Step 2: Compute h based on Eqn. 35

$\begin{matrix}{h = {\sqrt{\frac{6\; M_{0}}{b\;\sigma_{\max}}} = \sqrt{\frac{6\; T_{\max}}{b\;\sigma_{\max}}}}} & {{Eqn}.\mspace{14mu} 36}\end{matrix}$

Step 3: If h is unreasonable for the application, pick a new b andrepeat step 2; otherwise proceed to step 4.

Step 4: Compute l

$\begin{matrix}{l = \frac{{Ebh}^{3}}{12\; k}} & {{Eqn}.\mspace{14mu} 37}\end{matrix}$

Low Inertia Shuttle

Returning back to Eqn. 22, it was illustrated that the energy loss dueto engagement of the clutch is proportional to the inertia of theshuttle. Thus it is advantageous to minimize inertia of the shuttle. Asseen in FIG. 3A, one end of the torsion spring 431 may be coupled to theshuttle 425 and may move with it. For convenience, the end of the springcoupled to the shuttle may be called the “inboard end”. The other end ofthe spring may be coupled to the spring case 435. For convenience, theend of the spring coupled to the spring case may be called the “outboardend”. The outboard end of the spring may move relatively slowly comparedto the inboard end. Thus the inertia of the inboard end of the springmay contribute to the energy loss to the same extent as the inertia ofthe shuttle however the inertia of the outboard end may have adiminished influence on the energy loss. In examples below, thedifference between the inboard end and the outboard end are exploited.In other examples, the shuttle size is made smaller so that it may weighless thus making its inertia smaller.

FIG. 9A illustrates the example of a drive mechanism with a shuttle thathas low inertia and one where the difference of inertia between theinboard end and outboard end of a spring is exploited. FIG. 9Aillustrates this example in relation to the class D mechanical analogalthough the same approaches may be applied to the buck circuitmechanical analog as well. FIG. 9A shows a cross-section of the device1200. In FIG. 9A, the shuttle is depicted by 1205. The shuttle may becoupled to one side of two one-way clutches 1210A and 1210B. The inputhubs are illustrated as 1215A and 1215B and may be coupled to theopposite side of the one-way clutches 1210A and 1210B. The input hubsmay also be coupled to an external actuator such as constant spendmotor. As described earlier, one input hub may rotate in the directionof the external motor while the other may rotate in the oppositedirection as a reversing gear may be present between the output of theexternal motor and the input hub. The coupling of an external motor tothe input hubs is illustrated by gears 1220A and 1220B. The rotation ofthe input hubs may be coupled to the shuttle by various mechanismsincluding but not limited to electrolaminate disc clutch, or amechanically or electrolaminate activated wrap spring clutch. In theFigure, wrap spring clutches are illustrated. Springs 1225A and 1225Bare shown respectively coupling input hubs 1215A and 1215B to theshuttle 1205. The springs 1225A and 1225B each wrap around theirrespective input hubs and one end of the shuttle. For example, spring1225A wraps over the input hub 1215A and the left section of the shuttle1205 in such a way that if the input hub rotates, spring 1225A willrotate along with it and wrap down on the left section of the shuttle,consequently imparting rotation to the shuttle in the same direction asthe input. While noting that the other input hub 1215B may be rotatingin the opposite direction as input hub 1215A, spring 1225B impartsmotion to the right section of the shuttle in a similar manner. Eachspring may have a tab 1228A and 1228B which may be coupled immovably torings 1227A and 1227B respectively. Rings 1227A and 1227B may be gearedand may be coupled to the input hubs so that they may either move withor slip over the input hub if held in place. The gears of rings 1227Aand 1227B engage with engagement mechanisms 1229A and 1229B. Thefunction of the rings 1227A and 1227B along with the engagementmechanisms 1229A and 1229B will now be described with the help of FIG.9B which shows a front view of a section of the ring 1227A along withthe engagement mechanism 1229A. The other ring and engagement mechanismare identical and are not shown. The engagement mechanism may be causedto move in a bidirectional manner along the arrow 1276. The engagementmechanism may engage with the teeth of the geared ring and may stop thering from rotating. Alternatively, the engagement mechanism may bepositioned away from the geared ring allowing the ring to rotate.

Returning back to FIG. 9A, when for example the engagement mechanism1229A engages with the ring 1227A, the tab of spring 1225A is held inplace and the spring is unable to wind down on the input hub 1215A. Whenthis occurs, no rotation is imparted to the shuttle. When the engagementmechanism 1229A disengages from the ring 1227A, the tab 1228A is nolonger held in place and the spring is able to clamp down on the inputhub and the shuttle, causing the rotation of the input hub to beimparted to shuttle. The operation of the engagement mechanism 1229B andring 1227B is exactly identical and will not be described. Theengagement mechanisms 1229A and 1229B may be activated in one of manywell-known ways including but not limited to mechanical means bysuitable motors or electromagnetical means by solenoids. Thus with themechanisms above, rotation may be imparted to the shuttle.

Shuttle 1205 may be immovably coupled to a tube 1265 which may besupported and may rotate within the housing of device 1200 on bearingssuch as 1238. For clarity only some of the bearings are enumerated. Thehousing is indicated by 1232 and appears on both sides of the shuttle.The housing may be an independent member or it may be part of a largersystem such as the frame of a robot. The tube 1265 may have two parts1235 and 1240. Section 1235 of the tube 1265 which is shown in theFigure generally to the left of the shuttle may provide mechanicalsupport for the shuttle and the input hub 1215A to rotate on. Thus as isillustrated in the Figure, the input hub 1215A may rotate on the tubesection 1235 on bearings. Section 1240 of the tube 1265 shown in theFigure generally to the right of the shuttle, may be a tubular torsionspring. The shuttle, the tube section 1235 and the tube section 1240 mayall physically be one piece, but each member may be made of differentcomponents. Additionally, both sections 1235 and 1240 of the tube 1265may provide the structure to locate the snap rings 1230A and 1230B.These snap rings may provide the means to keep the input hubs and theshuttle in place. Section 1235, as stated earlier is merely a tube withno spring like qualities; hence it may rotate just like the shuttlerotates. However, again as stated earlier, section 1240 may be a tubulartorsion spring and its operation will be described below.

As may be seen in the Figure, section 1240 of the tube 1265, extendsfrom the shuttle to another hub 1245. For convenience, the hub 1245shall be called the “intermediate hub”. The intermediate hub 1245 may beconnected to a torsion spring 1255 which may be subsequently enclosed ina spring case 1250. The spring case may be supported by bearings 1238 onthe intermediate hub. The spring case may be coupled to an output gearor hub 1260. The gear 1260 may drive another gear 1275 which may formthe final output hub of the device 1200 and may be coupled to a load.The output gear may be supported by bearings on the housing 1232. Thehousing supporting the output gear may be the same as the housingsupporting the shuttle and the input hubs or it may be different.

The operation of the device 1200 is now described. Springs 1225A and1225B may be activated in the same manner as described earlier in FIG.2. Thus by applying an appropriate sequence of engagement anddisengagement of the springs 1225A and 1225B, the shuttle 1205 may becaused to rotate at a desired speed and direction. However, the shuttlein this device may be smaller particularly in the breadth dimension thanthe shuttle in FIG. 3A. The breadth dimension is illustrated by arrow1271 in the Figure. The smaller shuttle has a lower weight, lowering theinertia and consequently diminishing the energy loss during process ofengagement of the springs 1225A and 1225B. In addition, the shuttle iscoupled to a torsion tube 1240 instead of a torsion spring as in FIG.3A, which has implications for the inertia and therefore the energyloss. As is well known in the art, torsion tubes typically store moreenergy than a torsion spring for a given weight. This implies that theweight of the torsion tube coupled to the inboard section of the shuttlemay be less than that of a torsion spring that may be coupled to thesame shuttle, given that both the torsion tube and torsion spring arerequired to store the same energy. As stated earlier, the inboardsection of the spring contributes to the energy loss as the shuttle, butby using a torsion tube of lesser weight, energy loss is diminished. Inaddition, as illustrated in the Figure, the outboard section of thedevice where a torsion spring may be used, may be partially isolatedfrom the shuttle. Despite the weight of the torsion spring, its effecton the shuttle inertia may be diminished. It may now be seen that byusing a torsion tube, a smaller shuttle may be used and the differencebetween the inboard and outboard section of the spring may be exploitedto provide a device where the energy loss is diminished.

As is well known, although a torsion tube stores energy more efficientlythan a torsion spring, the length of torsion tubes may be long. Also asis well known, the torsion tube, in part due to its length, may besusceptible to buckling. Hence in some examples, support structures suchas but not limited to ribs may be coupled to the torsion tube to preventbuckling. In FIG. 9A, the ribs are indicated by 1280. These supportstructures may be placed on the outside of the tube or, in some otherconfigurations, they may be placed on the inside of the tube. There maybe one or several support structures.

In some applications, it may not be convenient to incorporate a longtorsion tube. In FIG. 9A, the length of the torsion tube is indicated bythe arrow 1272. Hence another example is described below where thelength of the tube may be made smaller. FIG. 9C illustrates such aexample. FIG. 9C illustrates a coaxial torsion tube. Only part of thetorsion tube is illustrated. The Figure illustrates a tube with threesections although more sections may be present. Section 1310 may becoupled to the shuttle 1205 just as torsion tube 1240 may be coupled tothe shuttle in FIG. 9A. Section 1310 may have a flange 1315 asindicated. The flange section may have holes such as a threaded holes toaccommodate a screw or a nut. A second section 1320, also a torsiontube, with flanges 1325 and 1326, one on either side, may be arrangedcoaxially over the first section. The flanges of section 1320 may againhave holes such as threaded holes as well, similar to the holes ofsection 1310. The second section is placed such that its predominantlength direction is backwards compared to the predominant lengthdirection of section 1310. The first and second section may be coupledby a circular plate 1335 which may have holes to accommodate screws ornuts. Nuts such as 1340 may be utilized to couple the first and secondsections. The front view of the plate 1335 is shown in FIG. 9D where theholes are shown by 1341. Only one hole is enumerated. A third sectionwhich may again be a torsion tube, may be similarly coaxially coupled tothe second section except now the coupling plate 1345 may be a ring asshown in FIG. 9E. In FIG. 9C, the third section is coupled to theintermediate hub 1245 of FIG. 9A. However, in some examples, there maybe more than three sections. FIG. 9C illustrates each section withsimilar wall thicknesses but in other examples, the wall thickness ofeach segment may be different. In addition, although FIG. 9C does notillustrate the anti-buckling support features, they may be present inthis configuration of FIG. 9C as well. In general, FIG. 9C illustratesthat by utilizing coaxial tubes, the projected length illustrated byarrow 1350 may be less than the length illustrated by arrow 1272 in FIG.9A. The projected length ignores the fold-back features of 1300. Thus,in applications where a shorter distance between the input and outputsections are required, the configuration of FIG. 9C may be utilized.

Electrically Controllable Engagement Mechanisms

FIGS. 10A and 10B are diagrams illustrating examples of electrolaminateclutches that may be used as electrically controllable clutches, such asclutches 319A and 319B in FIG. 2B, 415A and 415B in FIG. 3A, and 1010Aand 1010B in FIG. 7A. Various means may be utilized to increase theeffective coupling in electrically controllable clutch devices. As oneof ordinary skill in the art will appreciate, a variety of electricallycontrollable coupling techniques may be adapted for use in differentexamples of electrically controllable transmissions.

For example, electro-laminate effect, electroadhesion, electrostaticgripping and related terms generally refer to the mechanical coupling oftwo objects using electrostatic forces. Electroadhesion, as describedherein, uses electrical control of electrostatic forces to permittemporary and detachable attachment between two objects. Thiselectroadhesion holds two surfaces of these objects together orincreases the traction or friction between two surfaces due toelectrostatic forces created by an applied electric field. Thecharacteristics of electroadhesion generally include low slippage, highshear force and low peel-off force when de-activated.

In one example of an engagement technique between the discs of theclutches described above, electro-laminate effect depends on theelectrostatic forces between surfaces, between the clutch discs in thiscase, to achieve clamping between the discs. For example, facingsurfaces of discs 416 and 417 in FIGS. 10A-B may form the twoelectrolaminate surfaces. These arrangements provide for the clutch 415to be controllably and reversibly engaged. In one approach,electroadhesion or electrically controlled reversible adhesion may beobtained by applying a voltage difference, such as a high level DCvoltage, between facing surfaces of discs 416 and 417 in FIGS. 10A-B, toproduce electrostatic attractive forces that increase traction betweenthe discs. For example, voltage control circuit 1380 of FIG. 11 iselectrically coupled to the discs 416 and 417 and applies a high voltagepotential to induce in them the electro-laminate effect and clamp themtogether.

FIGS. 10A and 10B illustrate examples of electroadhesion whereelectrodes are provided in one of the discs 416 and 417 and anelectroadhesion voltage is applied to those electrodes to increasetraction between the discs. In the example of FIG. 10A, disc 417 isprovided with at least one pair of adjacent electrodes 1350 and 1352,which are electrically isolated from one another, where, for example,each electrode is a loop of conductive material embedded in disc 417.Note that multiple pairs of electrodes may be provided in disc 417, asillustrated in the example of FIG. 10A. An electrostatic adhesionvoltage produced by, for example, voltage conditioning circuit 1386, hasalternating positive and negative voltages that are applied to adjacentelectrodes 1350 and 1352 to create an electroadhesion effect. Thevoltage may be applied to electrodes 1350 and 1352 through a variety oftechniques, such as rings and brushes, which will be readily understoodby one of ordinary skill in the art.

As a result of the voltage difference between electrodes 1350 and 1352,an electric field forms in a dielectric surface of disc 417. Theelectric field locally polarizes the dielectric material and thus causeselectrostatic adhesion between the electrodes 1350 and 1352 and disc 417and the induced charges in the dielectric material of disc 416. Theinduced charges may be the result of the dielectric polarization or fromweakly conductive materials and leakage currents, though the examples ofelectrically controllable engagement techniques is not limited by theexamples illustrated. For example, the induced electrostatic forces mayalso use the Johnson-Rahbeck effect to provide increased forces at lowerpower levels.

Thus, the electrostatic adhesion voltage provides an electrostatic forcebetween the disc 417 and the material beneath the surface of disc 416 toincrease the traction between them and engage the clutch 415. Removal ofthe electrostatic adhesion voltage ceases the electrostatic adhesionforce between discs 416 and 417, which reduces the traction between themand disengages the clutch. The electrostatic adhesion voltage is appliedto engage the discs of the clutch during on time intervals and removedfrom the discs to disengage the discs during off time intervals, such asthose described above with respect to the waveforms of FIGS. 2C-K, FIG.4, and FIG. 5A.

FIG. 10B illustrates another example, wherein one or more pairs ofadjacent electrodes 1350 and 1352 are provided in disc 416. Anelectrostatic adhesion voltage applied to electrodes 1350 and 1352 formsan electric field in a dielectric surface of disc 416 that locallypolarizes the dielectric material of disc 417 and causes electrostaticadhesion between the electrodes 1350 and 1352 and disc 416 and theinduced charges in the dielectric material of disc 417. Thus, tractionbetween discs 416 and 417 may be electrically controlled by theselective application of the electrostatic adhesion voltage toelectrodes 1350 and 1352.

FIG. 11 illustrates one simplified example of a voltage control circuit1380, wherein a control circuit 1382, which may be a microprocessor ormicrocontroller, for example, controls conditioning circuit 1386, whichmay condition the electrostatic adhesion voltage signal applied to thediscs of a clutch via electrodes 1350 and 1352. A power source 1384,such as a battery or power supply, for example, provides operating powerfor the voltage control circuit 1380 and provides the power for theelectrostatic adhesion voltage signal applied to the electrodes. Controlcircuit 1382 may engage the transmission by causing conditioning circuit1386 to output the electrostatic adhesion voltage to the discs of theclutch and disengage the transmission by causing conditioning circuit1386 to stop generating the electrostatic adhesion voltage. Thisarrangement provides for the discs of the clutches described above, suchas discs 416 and 417 of clutch 415 in FIG. 10B, to be controllably andreversibly coupled under control of voltage control circuit 1380.

In some embodiments, electroadhesion as described herein permits fastengagement and disengagement times and may be considered almostinstantaneous. The speed of engagement and disengagement may beincreased by several means. If the electrodes are configured with anarrower line width and closer spacing, then speed is increased usingconductive or weakly conductive substrates, e.g the clutch disc 416 or417 that does not include electrodes, because the time needed for chargeto flow to establish the electroadhesive forces is reduced. Basically,the RC time constant of the distributed resistance-capacitance circuitincluding both electroadhesive device, e.g. the disc 416 or 417 thatincludes electrodes, and substrate is reduced. It is also possible touse higher voltage to establish a given level of electroadhesive forcesmore quickly, and one can also increase speed by overdriving the voltagetemporarily to establish charge distributions and adaptations quickly.To increase disengagement speeds, a driving voltage that effectivelyreverses polarities of electrodes at a constant rate may be employed.Such a voltage prevents charge from building up in the dielectricsubstrate material and thus allows faster disengagement. Alternatively,a moderately conductive material can be used between the electrodes toprovide faster discharge times at the expense of some additional drivingpower required. These forms of electrostatic adhesion voltage may beapplied to engage the discs of the clutch during the on time intervalsand removed from the discs to disengage the discs during the off timeintervals described above with respect to the waveforms of FIGS. 2C-K,FIG. 4, and FIG. 5A.

As the term is used herein, an electrostatic adhesion voltage refers toa voltage that produces a suitable electrostatic force to couple anelectroadhesive device, e.g. a disc with electrodes, to substrate, e.g.a disc with a dielectric surface material. The minimum voltage neededfor the electroadhesive device will vary with a number of factors, suchas: the size of the electroadhesive device, the material conductivityand spacing of the electrodes, the insulating material betweenelectrodes, the dielectric surface material, the presence of anydisturbances to electroadhesion such as dust, other particulates ormoisture, the weight of any structures mechanically coupled to theelectroadhesive device, compliance of the electroadhesive device, thedielectric and resistivity properties of the substrate, and the relevantgaps between electrodes and substrate. In one embodiment, theelectrostatic adhesion voltage includes a differential voltage betweenthe electrodes that is between about 500 volts and about 10 kilovolts.In a specific embodiment, the differential voltage is between about 2kilovolts and about 5 kilovolts. Voltage for one electrode can be zero.Alternating positive and negative charges may also be applied toadjacent electrodes.

Returning to the example of FIG. 11, control circuitry 1380 isconfigured to determine when a suitable electrostatic adhesion voltageis applied to electrodes 1350 and 1352. Circuitry 1380 may include aprocessor or controller 1382 that provides on/off signals that determinewhen electrostatic adhesion voltages are applied and some of thecharacteristics of the voltage signal, such as magnitude. Circuitry 1380may also determine the times associated with a charge and dischargecycle on the electroadhesive device. Examples of on/off signal schemesthat may be generated under the control of control circuit 1382 areillustrated and described above in the context of FIGS. 2C-K, FIG. 4,and FIG. 5A.

Conditioning circuitry 1386 may include any circuitry configured toperform one or more of the following tasks: voltage step-up, which isused when applying a voltage to the electrodes 1350 and 1352, conversionbetween AC and DC power, voltage smoothing, and recovery of storedelectrostatic energy. Conditioning circuitry 1386 may be designed toreceive power from a low-voltage battery if such a battery is used aspower source 1384. For example, in robotics applications, conditioningcircuitry 1386 may receive a voltage from a conventional battery, suchas those less than 40 volts, and increase the voltage to anelectrostatic adhesion voltages above 1 kilovolt. The low voltage powersource such as the battery may be replaced by another electrical sourcesuch as a small photovoltaic panels similar to the ones used in manyhandheld calculators. In one embodiment, conditioning circuitry 1386includes a transformer or switching power supply configured to providevoltage step-up to electrostatic adhesion voltages described herein. Ina specific embodiment, conditioning circuitry 1386 includes a model No.Q50-5 as provided by EMCO High Voltage Corporation of 70 Forest ProductsRoad, Sutter Creek Calif. Conductive leads extend from conditioningcircuitry 1386 to electrodes 1350 and 1352.

More complex charge control circuits may be developed, depending on theconfiguration of the electroadhesive device and are not limited to theexample of FIG. 11. Also, some of the circuit functions may beintegrated. For instance, one integrated circuit may perform the controlof control circuit 1382 and of conditioning circuitry 1386.

The voltages provided to the electroadhesive devices may vary. In oneembodiment, AC actuation is applied to the electrodes. In some cases,electrostatic forces on a dielectric substrate may relax over a timeconstant under steady DC actuation. This phenomena can also occur in aninsulator if it traps charge. However, by alternating the polarity ofcharge on each of the electrodes at a high frequency, electroadhesiveforces can be maintained or even enhanced. In a specific embodiment, theAC signal includes a frequency above 1 Hz. Other higher and lowerfrequencies may be used. In another embodiment, multiple sets ofelectrodes are used with applied AC voltages offset in time or shiftedin phase. This allows one set of electrodes to maintain electroadhesiveforces while the AC voltage in another set temporarily passes through 0voltage difference. In another embodiment, a DC actuation may beprovided to the electrodes. In some of the cases with DC actuation, amoderately low insulator resistance may provide a leakage path toachieve a fast release when voltage is switched off. In other cases, afixed amount of charge of opposite polarity to the DC actuation may bepulsed into the electrodes to provide release when desired. In thiscase, the fixed amount of charge may come from an external capacitor orone that is a part of the conditioning circuitry 1386 with a capacitanceequal to that of the electroadhesive device, e.g. the discs of anelectrically controllable clutch.

Switching and response times of an electroadhesive device will vary withthe electrical equipment and signal applied to the electrodes. Forexample, a 5 Hz signal, with a voltage rise time of one-tenth of thetime period, may provide a charge and discharge cycle of 20milliseconds.

In general, electroadhesion requires a small amount of power to increasetraction between an electroadhesive device, e.g. a disc with electrodes,and a dielectric substrate, e.g. a dielectric disc. The powerrequirement is small because electroadhesion may be primarily thought ofas a capacitive effect. This implies that with appropriate selection ofinsulation material to minimize leakage currents, the reactive powerremains small. Resistivity of insulating material may be reduced iftrapped charge becomes a problem as long as the leakage current remainsacceptable.

Further information regarding some electrostatic adhesion voltages thatmay be suitable for use in various examples of electrically controllablepower transmission as described herein are described in commonly ownedU.S. Pat. No. 7,551,419 for “Electroadhesion”, as well as U.S. Pat. Nos.7,554,787 and 7,773,363 and U.S. Published Application No. 20130010398hereby incorporated in their entirety for all purposes.

Other examples of electrostatic techniques may be adaptable for use inthe presently described electrically controllable transmissions. Forexample, electrostatic gripping has been utilized in a variety ofindustries, including semiconductor manufacturing, for many years,examples of which are shown in U.S. Pat. No. 5,103,367 for“Electrostatic Chuck Using A.C. Field Excitation”, U.S. Pat. No.5,325,261 for “Electrostatic Chuck with Improved Release”, and U.S. Pat.No. 6,922,324 for “Remote Powering of Electrostatic Chucks”.

Other forms of electrically controllable coupling may possibly beadapted for use in the examples of electrically controllabletransmissions discussed herein, such as eddy current braking describedin U.S. Pat. No. 7,592,727 for “Quiet Load for Motor Testing” or theinductive coupling described in U.S. Pat. No. 5,856,710 for “InductivelyCoupled Energy and Communication Apparatus”. Another electricallycontrollable coupling approach that may be adapted in some examplesincludes magnetic coupling, where, for example, a disc withelectromagnets adjacent its outer surface that engages electromagnets inanother disc and the electromagnets are configured to have alternatingpolarity to provide torque transfer between the discs. Furtherinformation regarding magnetic coupling is described at MagneticallyCoupled Drive—OpenROV R&D(https://forum.openrov.com/t/magnetically-coupled-drive/30) and magneticgearing techniques, an example of which is described in U.S. Pat. No.5,569,967 for “Magnetic Gear and Gear Train Configuration”. Thesereferences are also incorporated by reference in their entirety for allpurposes.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and/or were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thespecification and in the following claims are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The terms “having,” “including,”“containing” and similar referents in the specification and in thefollowing claims are to be construed as open-ended terms (e.g., meaning“including, but not limited to,”) unless otherwise noted. Recitation ofranges of values herein are merely indented to serve as a shorthandmethod of referring individually to each separate value inclusivelyfalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orclearly contradicted by context. The use of any and all examples, orexemplary language (e.g., “such as”) provided herein, is intended merelyto better illuminate embodiments of the invention and does not pose alimitation to the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to each embodiment of the presentinvention.

Different arrangements of the components depicted in the drawings ordescribed above, as well as components and steps not shown or describedare possible. Similarly, some features and subcombinations are usefuland may be employed without reference to other features andsubcombinations. Embodiments of the invention have been described forillustrative and not restrictive purposes, and alternative embodimentswill become apparent to readers of this patent. Accordingly, the presentinvention is not limited to the embodiments described above or depictedin the drawings, and various embodiments and modifications can be madewithout departing from the scope of the invention.

We claim:
 1. A system, comprising: an electrically controllabletransmission, wherein the electrically controllable transmissioncomprises a first input hub and a second input hub, a first electricallycontrollable clutch and a second electrically controllable clutch, arotatable member, an output hub, and a bias member that couples therotatable member to the output hub, wherein the first electricallycontrollable clutch is configured to transmit power between the firstinput hub and the rotatable member when engaged, and wherein the secondelectrically controllable clutch is configured to transmit power betweenthe second input hub and the rotatable member when engaged; and acontrol circuit configured to apply at least one control signal to atleast one electrically controllable clutch of the first and secondelectrically controllable clutches, wherein the at least one controlsignal comprises pulses that cause the at least one electricallycontrollable clutch to engage and disengage in at least one sequence ofalternating engagement time intervals and disengagement time intervals,wherein a transmission ratio of the electrically controllabletransmission is controlled by the at least one sequence of alternatingengagement time intervals and disengagement time intervals.
 2. Thesystem of claim 1, wherein the control circuit is further configured toadjust the transmission ratio of the electrically controllabletransmission by adjusting at least one of a width of the pulses or afrequency of the pulses.
 3. The system of claim 1, wherein the at leastone control signal comprises pulses that cause the first electricallycontrollable clutch to engage and disengage in a first sequence ofalternating engagement time intervals and disengagement time intervals,wherein the transmission ratio of the electrically controllabletransmission is controlled by the first sequence of alternatingengagement time intervals and disengagement time intervals.
 4. Thesystem of claim 3, further comprising a one-way clutch that couples therotatable member to a stationary chassis.
 5. The system of claim 3,wherein the bias member comprises a spring.
 6. The system of claim 5,wherein the spring exchanges energy with the first input hub and theoutput hub when the first electrically controllable clutch is engagedand exchanges energy with the output hub when the first electricallycontrollable clutch is disengaged.
 7. The system of claim 5, wherein thespring stores energy by winding and releases energy by unwinding.
 8. Thesystem of claim 1, wherein the first input hub is configured to bedriven in a first rotational direction and the second input hub isconfigured to be driven in a second rotation direction that is oppositethe first rotational direction.
 9. The system of claim 1, furthercomprising: a first one-way clutch, wherein the first one-way clutch isconfigured to couple the first input hub to the rotatable member; and asecond one-way clutch, wherein the second one-way clutch is configuredto couple the second input hub to the rotatable member.
 10. The systemof claim 1, wherein the at least one control signal comprises a firstcontrol signal and a second control signal, wherein the first controlsignal comprises pulses that cause the first electrically controllableclutch to engage and disengage in a first sequence of alternatingengagement time intervals and disengagement time intervals and thesecond control signal comprises pulses that cause the secondelectrically controllable clutch to engage and disengage in a secondsequence of alternating engagement time intervals and disengagement timeintervals, and wherein the transmission ratio of the electricallycontrollable transmission is controlled by the first sequence ofalternating engagement time intervals and disengagement time intervalsand the second sequence of alternating engagement time intervals. 11.The system of claim 10, wherein the first electrically controllableclutch is disengaged when the second electrically controllable clutch isengaged, and wherein the second electrically controllable clutch isdisengaged when the first electrically controllable clutch is engaged.12. The system of claim 10, wherein the bias member comprises a spring.13. The system of claim 12, wherein the spring stores energy by windingand releases energy by unwinding.
 14. The system of claim 10, whereinthe spring exchanges energy with the first input hub and the output hubwhen the first electrically controllable clutch is engaged and exchangesenergy with the second input hub and the output hub when the secondelectrically controllable clutch is engaged.
 15. The system of claim 1,wherein the at least one electrically controllable clutch comprises atleast one of an electrolaminate disc clutch, an electrolaminateactivated wrap spring clutch, or an electromagnetically activated wrapspring clutch.
 16. The system of claim 1, wherein the bias membercomprises a torsion spring.
 17. The system of claim 1, wherein the biasmember comprises a torsion tube.